Lamp drive circuit for driving a number of lamps and balancing currents flowing through the lamps

Abstract

A lamp drive circuit used for driving a number of lamps is provided. The lamps are used in the backlight module. The backlight module is used for providing a light source when a liquid crystal display displays. The lamps are respectively electrically connected to a coil. The coils substantially have the same coil turns and have the same magnetic circuit, so that the currents flowing through the lamps are balanced.

1. A lamp drive circuit for driving a plurality of lamps including a first lamp and a second lamp, the lamp drive circuit comprising:
 a power supply circuit including a first output terminal for outputting a first alternate voltage and a second output terminal for outputting a second alternate voltage; and 
 a balance circuit, coupled to the first and second output terminals, for driving at least the first lamp and the second lamp, the balance circuit including:
 a first coil, having one end coupled to the first output terminal and the other end coupled to the first lamp; 
 a second coil, having one end coupled to the second output terminal and the other end coupled to the second lamp, wherein a voltage across the first coil corresponds to a voltage across the second coil; 
 a first core, 
 a second core, 
 a third coil, having coil turns substantially equal in number to the coil turns of the first coil, the third coil and the first coil both wound around the first core, and 
 a fourth coil, the third coil and the fourth coil forming a closed loop, the coil turns of the fourth coil being substantially equal in number to the coil turns of the first coil, the fourth coil and the second coil both being wound around the second core, wherein the coil turns of the first coil are substantially equal in number to the coil turns of the second coil; 
 
 a feedback circuit for outputting a feedback signal according to a voltage difference between one end of the third coil and one end of the fourth coil, wherein the power supply circuit further includes:
 an energy converter for outputting an alternating current signal, 
 a transformer for outputting the first alternate voltage and the second alternate voltage according to the alternating current signal, and 
 a controller for controlling the energy converter to output the voltage level of the alternating current signal according to the feedback signal. 
 
 
     
     
       2. The lamp drive circuit according to  claim 1 , wherein the balance circuit further includes a capacitor coupled to the other end of the first coil and the other end of the second coil. 
     
     
       3. The lamp drive circuit according to  claim 1 , wherein the balance circuit further includes:
 a first capacitor, wherein the other end of the first coil is coupled to a fixed voltage via the first capacitor, and 
 a second capacitor, wherein the other end of the second coil is coupled to the fixed voltage via the second capacitor. 
 
     
     
       4. The lamp drive circuit according to  claim 1 , wherein the energy converter outputs the alternating current signal according to an alternating electric supply. 
     
     
       5. The lamp drive circuit according to  claim 1 , wherein the balance circuit further includes:
 a core, wherein the first coil and the second coil are both wound around the core, and the coil turns of the first coil are substantially equal to the coil turns of the second coil. 
 
     
     
       6. The lamp drive circuit according to  claim 5 , wherein an impedance of the first coil corresponds to an impedance of the first lamp, and an impedance of the second coil corresponds to an impedance of the second lamp. 
     
     
       7. The lamp drive circuit according to  claim 5 , wherein the balance circuit further includes:
 a first inductor, 
 a first capacitor, wherein the other end of the first coil is coupled to one end of the first inductor via the first capacitor, and 
 a second capacitor, wherein the other end of the second coil is coupled to the other end of the first inductor via the second capacitor. 
 
     
     
       8. The lamp drive circuit according to  claim 1 ,
 wherein the energy converter is a DC-to-AC converter. 
 
     
     
       9. The lamp drive circuit according to  claim 8 , wherein the feedback circuit includes:
 a full-wave rectifying circuit for rectifying and outputting the voltage difference, and 
 a filter for filtering noise of the rectified voltage difference to become the feedback signal. 
 
     
     
       10. The lamp drive circuit according to  claim 8 , wherein the feedback circuit includes:
 a half-wave rectifying circuit for rectifying and outputting the voltage difference, and 
 a filter for filtering noise of the rectified voltage difference to become the feedback signal. 
 
     
     
       11. A lamp drive circuit for driving a plurality of lamps including a first lamp, a second lamp, a third lamp, and a fourth lamp, the lamp drive circuit comprising:
 a power supply circuit including a first output terminal for outputting a first alternate voltage and a second output terminal for outputting a second alternate voltage; and 
 a balance circuit, coupled to the first and second output terminals, for driving at least the first lamp and the second lamp, the balance circuit including:
 a first coil, having one end coupled to the first output terminal and the other end coupled to the first lamp; 
 a second coil, having one end coupled to the second output terminal and the other end coupled to the second lamp, wherein a voltage across the first coil corresponds to a voltage across the second coil; 
 a first core, 
 a second core, 
 a third core, 
 a fourth core, 
 a third coil, having coil turns substantially equal in number to the coil turns of the first coil, the third coil and the first coil being both wound around the first core; 
 a fourth coil, having one end receiving the first alternate voltage and the other end outputting a third current to the third lamp, the coil turns of the fourth coil being substantially equal in number to the coil turns of the first coil; 
 a fifth coil, having coil turns substantially equal in number to the coil turns of the fourth coil, the fifth coil and the fourth coil both being wound around the second core, 
 a sixth coil, the sixth coil and the fifth coil forming a closed loop, the coil turns of the sixth coil being substantially equal in number to the coil turns of the fifth coil, the sixth coil and the second coil both being wound around the third core, 
 a seventh coil, having one end receiving the second alternate voltage and the other end outputting a fourth current to the fourth lamp, and the coil turns of the seventh coil are substantially equal in number to the coil turns of the second coil, and 
 an eighth coil, the eighth coil and the third coil forming a closed loop, the coil turns of the eighth coil being substantially equal in number to the coil turns of the seventh coil, and the eighth coil and the seventh coil are both wound around the fourth core; wherein the coil turns of the first coil are substantially equal in number to the coil turns of the second coil. 
 
 
     
     
       12. The lamp drive circuit according to  claim 11 , wherein the balance circuit further includes:
 a first capacitor coupled to the other end of the first coil and the other end of the fourth coil, and 
 a second capacitor coupled to the other end of the second coil and the other end of the seventh coil. 
 
     
     
       13. The lamp drive circuit according to  claim 11 , further comprising a feedback circuit for outputting a feedback signal according to a voltage difference between one end of the third coil and one end of the eighth coil, wherein the power supply circuit further includes:
 an energy converter for outputting an alternating current signal, 
 a transformer for outputting the first alternate voltage and the second alternate voltage according to the alternating current signal, and 
 a controller for controlling the energy converter to output the voltage level of the alternating current signal according to the feedback signal. 
 
     
     
       14. The lamp drive circuit according to  claim 13 , wherein the energy converter outputs the alternating current signal according to an alternating electric supply. 
     
     
       15. The lamp drive circuit according to  claim 11 , further comprising a feedback circuit for outputting a feedback signal according to a voltage difference between one end of the third coil and one end of the eighth coil, wherein the power supply circuit further includes:
 a DC-to-AC converter for outputting an alternating current signal; 
 a transformer for outputting the first alternate voltage and the second alternate voltage according to the alternating current signal, and 
 a controller for controlling the DC-to-AC converter to output the alternating current signal according to the feedback signal. 
 
     
     
       16. The lamp drive circuit according to  claim 15 , wherein the feedback circuit includes:
 a full-wave rectifier circuit for rectifying and outputting the voltage difference; and 
 a filter for filtering noise of the rectified voltage difference to become a feedback signal. 
 
     
     
       17. The lamp drive circuit according to  claim 15 , wherein the feedback circuit includes:
 a half-wave rectifier circuit for rectifying and outputting the voltage difference; and 
 a filter for filtering noise of the rectified voltage difference to become the feedback signal.